This invention relates to control apparatus for electrical motors, and particularly to control apparatus for an electric motor for driving an intermittent drive mechanism in a flying spot television scanner apparatus.
A flying spot television scanner apparatus typically comprises a film transport mechanism including a driven take-up spool and a driven intermittent drive mechanism. Electric motors are provided for driving the take-up spool and the intermittent drive mechanism, and these motors are so controlled as to ensure that a film passes through a film gate in the transport mechanism at a rate of film frames per second which preserves the illusion of natural motion on the film and also enables each frame of the film to be scanned by two or more television scanning fields while ensuring that pull-down of the film between successive frames presented for scanning in the gate occurs only during a field blanking pulse of the television scanning. The scanning is accomplished by a point of light carrying out a television field scan on the picture area of a film frame in the gate. This point of light is produced by a cathode ray tube combined in the flying spot scanner apparatus with an optical system arranged to project an image of a raster area of the screen of the cathode ray tube on to the picture area in the gate. The cathode ray tube is coupled to television scanning and blanking circuits which in operation produce a television raster on the raster area of the tube screen.
In television in the United States, there are sixty fields per second and correspondingly sixty field blanking pulses per second. In the United Kingdom, there are fifty fields per second and fifty field blanking pulses per second.
The known flying spot television scanner apparatuses are restricted to scanning films whose intended frame rate is twenty-four frames per second. However, films intended to be shown at eighteen frames per second are produced in great numbers, and it is accordingly an object of the present invention to provide control apparatus for an electric motor which can be incorporated in a flying spot television scanner apparatus for twenty-four frame per second film or eighteen frame per second film.